(-2)^4 + (3)^-1=??

Which part are you having touble with? Can you evaluate (-2)^4? As for 3^-1, that is the inverse of 3^1 , that is, 1/(3^1). Then just add the two parts.

Here are some examples to help you:

(-3)^4 = 3^4 (raising to an even power makes it positive)

= 3*3*3*3 = 81

(4)^-1 = 1/(4^1) = 1/4

my question is 6.42X10^8+4.12X10^7

Adding these requires converting the 4.12 x 10^7 number into the equivalent using 10^8. Do you know how to do that? Then you can simply add. Here's an example that shows how to do this: consider 6.5 x 10^5 + 3.2 x 10^4. Change 3.2 x 10^4 to 0.32 x 10^5. Now you have 6.5+10^5 + 0.32 x 10^5 = (6.5 + 0.32) x 10^5 = 6.82 x 10^5. Hope this is clear.